I was lucky enough to be gifted 5g of Sourdough Starter (Gloria, the Glorious Sourdough Starter) by a friend;
Initially I fed Gloria, a ratio of 1:4:5 of starter:water:bread flour
So 20g water and 25g of flour.
Now I regularly take some out to make bread, feed that part 1:1:1 - e.g. 100g of starter:water:flour to make 300g starter for two loaves see Sourdough Loaf.
Then feed 50g:50g:50g: starter + water + flour to store in the fridge (after bubbling up!)
Tip: She doesn’t want to be airtight when you feed her and she’ll just need to be left at room temp somewhere and over the following few hours should start to bubble and grow!